In the transporting or shipment of temperature sensitive materials or items such as blood, plasma, vaccines and certain drugs, it is known to use insulated containers which include heating and/or cooling means as disclosed, for example in U.S. Pat. No. 5,483,799 and No. 5,603,220 and in U.S. Pat. No. 5,950,450 and No. 5,943,876 assigned to the assignee of the present invention and the disclosures of which are herein incorporated by reference. When it is desirable to transport or ship a larger volume of temperature sensitive items, it is desirable to provide a cargo container which is adapted to receive a pallet supporting the temperature sensitive items and which also includes cooling and/or heating means for maintaining the temperature sensitive items within a close predetermined temperature range. Such cargo containers are disclosed, for example, in U.S. Pat. Nos. 5,187,947, 6,860,115 and in a publication of applicants entitled AcuTemp™ Thermal Pallet Shipper. A Temperature-Controlled, Pallet-Sized Shipping Container is also disclosed in U.S. patent application No. 2004/0226309, published Nov. 18, 2004, and the disclosure of which is herein incorporated by reference. This published application claims the benefit of provisional application No. 60/447,987 filed Feb. 17, 2003 by four co-inventors including co-inventors of the present invention, and the disclosure of which is herein incorporated by reference.
In any such cargo container adapted to receive one or more pallets of temperature sensitive items, it is highly desirable for the container to have all walls and the doors with high thermal insulation or R value while minimizing the thickness of the walls in order to maximize the cargo space and minimize heat transfer to and from the container chamber. It is also desirable to provide efficient construction and assembly of the cargo container while providing substantial durability so that the cargo container has an extended service life. It is further desirable for temperature controlled air to be properly circulated within the cargo chamber in order to obtain a uniform temperature throughout the chamber. Preferably, the circulating air passes upwardly through a refrigeration evaporator and electrical heating elements and circulates along the walls of the container for precisely controlling the temperature within the cargo chamber.
In order for a cargo chamber to hold a narrow predetermined temperature range for an extended period of time, for example, over 72 hours, without an external power supply, it is necessary for the cargo container to carry storage batteries which may operate a refrigeration compressor or an electrical heating element through a control system which senses the temperature within the cargo chamber at predetermined locations. The heating element for the circulating air is sometimes desirable when the cargo container is being transported in a cold temperature zone or by an aircraft flying at a high altitude, and the container is exposed to very cold environmental air.